For those of you who, like me, get excited about structural engineering problems, the below pictures are interesting. To build an extension onto our penthouse terrace, the terrace itself had to be reinforced, as it does not have much in the way of structural support underneath. To do this, they criss-crossed strips of carbon fiber (apparently quite sturdy) on both sides of the floor, and ran steel cables between them. This should do the trick, according to our construction people.